Trouble Ripping 6/4 Soft Maple

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We make 1-7/16" thick x 2-1/2" wide x 27" long hardwood slats for industrial use, with some other milling in these. We use to use all Ash in 6/4 planed down to about 1-7/16" and had good luck with that. We are havving trouble getting the Ash now and have switched to #1 Soft Maple. Problem is that the pieces are closing up behind the blade so bad like nothing I have ever seen before. We all have some close up behind the blade here and there but this is every single piece we need to stop the saw and forcefully yank it back out of the blade. We have a spliter and added a second spliter a few inches back that made it worse. They are closing up so tight on the spliter we cant even force them through and its getting dangerous. So the last batch we pre-ripped on the bandsaw and finished on the tsaw works good but takes too long. Our table saw is a 10" under powered contractor saw with an upgraded motor/fence etc. No real riving knife. I am wondering if I upgraded to a larger tsaw with a good factory riving knife if this will really help??? Other lumber is fine. Just this 6/4 soft maple.

Get a bigger saw, a straight line rip would be best for this application but they are a little pricy. If you do this a lot I would get the rip saw, plenty of power and a built in power feed with some safety features no table saw can match.

Are you planing first? If not, the additional stress by running less flat stock through will make it worse.

Yes, an SLR would be the ideal, but you can easily make do with a decent table saw and a power feed. You will need to drill mounting holes but it's well worth it. We used a table saw with power feed for two decades before upgrading to an SLR. Biggest advantage of an SLR is that you don't have to joint one edge first. Other than that, a TS/PF will do a fine job compared to a single blade SLR.

Thanks for the reply's. Yes it is all planed flat to final thickness first and cut to final length. Is this what you would call "case hardened" lumber?

A straight line rip saw is out of the question right now. $$ I could do a 5hp large cabinet saw and eventually put a feeder on it?? With a factory riving knife this could power right through this stuff safely you think?

I would look to the lumber. If other species rip OK, but the Maple binds, it is drying stress.

Do a case hardening test on a few pieces of the Maple, and I'll bet lunch you have stress in your lumber. If so, call your vendor and tell them to send a truck. Be sure to show the test samples to them. They should know.

For a good description of the test and the meanings of the results, Google "Quality Control in Lumber Purchasing - Purdue Extension - FNR-132" by Dan Cassens. Or follow the link below. It is a PDF that is handy to save and use whenever this comes up.

Once when we were buying truckloads of Poplar from some new vendors, we would test from four boards before we even unloaded the truck. If even one board of the four had a problem, the whole load went back. They learned real fast to not ship a bad load. Their prices increased as a result and this made the local favorite that never sent us questionable stock our primary supplier again.

5HP with a 10-12" blade (the smaller the blade the more power you'll have) should have the power. The feeder is what will make it safe.

One other thing to consider is the blade. If you have a small side clearance you'll be more apt to get binding.

One final thought. When we use the TS to rip, if we're having trouble with binding we use a wedge. This is a piece of slightly tapered material, usually hard maple, similar to a shim you'd use for installing doors or windows. As soon as the piece exits the power feed, the tailer inserts the wedge into the kerf and pounds it all the way to the bottom. This almost always prevents binding. NOTE: DO NOT TRY THIS UNLESS YOU ARE USING A POWER FEED! IT COULD CAUSE A KICKBACK IF TRIED WITHOUT ONE!!

I think that David has the main issue identified correctly...casehardening stress (also called drying stress). It results when the kiln operation does not condition (also called stress relieve) the lumber properly at the end of the drying cycle.

You can test for this stress instantly by doing the following test: Take a piece about 8" wide and 24 to 30' long. Rip it right down the center to get two 4" wide pieces. Put these two pieces back together (minus the saw kerf). If there is stress, there will be a gap; with no stress, the pieces will fit back together with no gap. (Note that the prong test that many people use for stress is not appropriate for measuring lengthwise stresses; use the above test.)

Not that soft maple is easier to cut and requires less power than the ash you have been using, so I do not thick it is power or the saw blade if the problem is primarily with SM.

If indeed you do have stress when you run the test, have the person drying your lumber either check with me directly or have them read pp. 101 - 102 about longitudinal stress in DRYING HARDWOOD LUMBER (copy here in the archives at WOOD WEB or many other places). This is the bible about hardwood lumber drying. To get good stress relief also requires the lumber to be well equalized; hopefully the kiln operator is also doing that properly.

" Put these two pieces back together (minus the saw kerf). If there is stress, there will be a gap;"

Technically, yes. But I would challenge you to find any source that can can consistently provide full kiln loads of material that will not have "stress".

Certainly, a kiln operator can ruin a whole load by an improper schedule, but there is a percentage of every batch of green lumber that has stress in it inherently, and no amount of white glove handling will eliminate it. There is a big difference between case hardening and natural stress. One can be overcome and the other can't.

Just to clarify what I said about HP and blades, I wasn't implying that soft maple is harder to cut than ash. I was offering a partial solution to stalling the saw because of stress.

I just noted that there are three different responses here by people named David. So, my original posting should have said that David Sochar hit the nail on the head!

David Waldmann's last response about growth stresses is indeed correct. However, I have seldom seen growth stresses in soft maple, so I did not mention them; it would be interesting to hear from people who have seen SM growth stress and also if they see it more in silver or in red maple. However, stress could be present in SM in a few pieces, but not to the extent that we might see in yellow-poplar, many softwoods, and some other species.

Note that growth stresses will show up when sawing lumber in that the green lumber will have instant warp.

Unrelieved drying stress would typically be much larger than growth stress.

Also, note that the prong test for stress (see pp. 101-102) will almost never respond to growth stresses, so if the prong test shows stress, we do know that we have drying stress. The prong measures transverse or across the grain stress, but such stress is not what causes movement when ripping. However, if there is transverse stress, we do know that the lumber was not stress relieved as it is suppose to be.

Note that on page 102 of the suggested reading, the picture shows both a test for growth stress and a test for drying stress. Because growth stress is not evenly centered from edge to edge, cutting the small fingers, as illustrated, will show the fingers are erratic in how they curve, versus the more uniform curve from drying stress.

When doing the test of ripping a piece in half, if there is growth stress, one of the pieces might curve quite a bit while the other has no curve. With drying stress, the two pieces will each curve the same amount, but in opposite directions.

Finally, I have seen many, many loads of properly dried lumber that have no stress or so little stress that manufacturing of ripped pieces has no warping issues.

Where we commonly see problems is when the kiln operator has not equalized the lumber well enough prior to stress relief, or the steam used for stress relief has excessive super heat which prevents the high humidity required for stress relief from being achieved.

Note that the right column on p. 101, halfway down, has the procedure for checking stress relief while the kiln is operating. (Actually, the kiln is shut down for a few minutes for retrieving and cutting the wood sample, but further delay is not needed.) Without this test, the kiln operator will relieve stress for maybe 18 hours on every load. Yet, each load needs fine tuning on the time, so this test on p. 101 is how to determine when stress relief is done. (A well air dried load will require very little stress relief, while a load dried in the kiln from green will have quite a bit. Higher shrinking woods, like oak, will have more stress than lower shrinking woods like SM. This is why we need to customize the stress relief time for each load.)

"Note that growth stresses will show up when sawing lumber in that the green lumber will have instant warp."

That's very interesting. We've never dealt directly with green lumber, to know what happens as a particular board travels along that path to production.

However, what I do know is that with pretty good success I (or any of my seasoned employees) can can what board is going to display evidence of stress by how the grain looks. Hard to describe it, but you know it when you see it. My point is that it's in the wood, not the drying, but becomes evident after drying, as these pieces can be "flat as a board", or, more realistically, relatively flat and straight.

As for soft maple having less stress, I agree. We see approximately half the amount of stress related defect in soft versus hard maple, but interestingly enough, almost exactly the same as ash.

That is a lot of info. I only use about 6,000 bf a year. I buy my lumber from 3 different sawmills. One is the most expensive, I pay almost full retail. I can complain and return lumber there and we get good product, if we ask for it. Another is for exclusive hard maple, they have a lot and we use a lot and it is priced in the middle. The other is the lowest cost, wholesale. Usually less than half than the others. That is where the soft maple comes from, as well as our red oak, ash, and some others sometimes (which is all good product). They have on hand about a million bf and usually about a thousand foot minimum and it is strict wholesale. Luckily I buy often enough there I have a much smaller minimum. But I don't think I will demand they take this soft maple back. I might mention something about it to my salesman about the case hardening and see what he says. But I'm just a tiny little customer to them. They sell by the semi-load or container load and I may be more of a bother to them.

Are there any other tricks to working with this stressed lumber? Sounds like one is all for quality control of the lumber and the other is compromise with power?? As mentioned we have been pre-ripping it on the band saw and that really does help. The lumber is not moving at all after planing, just ripping. And it is dry, we test with a meter regularly.

A do agree that a SLR does an excellent job on stress free lumber. You would be best served, when buying a used one, to get it from someone that has reconditioned it. As they wear from use, they do need maintenance, I would guess that most used machines will need maintenance to bring them to top operating condition.

To complete the discussion about soft maple, there are two kinds of soft maple in the eastern U.S.- -silver and red. There is quite a bit of difference (10% to 30%) between the two. Here is a tabulation with silver first and red second.

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